1. Field of the Invention
The invention relates to an improved waterproof sunscreen composition.
2. The Related Art
Sunscreen formulations for use on human skin are well-known and many different types are commercially available to satisfy diverse consumer needs. For example, sunscreen formulations having different sun protection fact (SPF) values are available, thus allowing consumers to choose the amount of protection desired. SPF values range from zero upward with higher values indicating greater amounts of sun protection. SPF values of 2-4 indicate minimal sun protection, 4-6 indicate moderate sun protection, 8-15 indicate maximal sun protection and above 15 indicate ultra sun protection.
One important consideration when choosing a sunscreen is whether it resists coming off in water. Waterproof formulations can undergo about 80 minutes in water without significant SPF loss. The formulations can be especially desirable because they eliminate the need for reapplication after swimming, bathing or excessive perspiration.
A classical method of achieving waterproof properties is through the use of a hydrophobic resin. For instance, U.S. Pat. No. 4,897,259 (Murray et al) discloses success through use of copolymers of polyvinylpyrrolidone (PVP) and long alkyl chain olefins, commonly referred to as alkylated PVP's. Besides a sunscreen agent and the copolymer, a variety of other functional ingredients are incorporated including emulsifiers, two of which are stated to be phosphated esters and polyoxyethylene fatty ester phosphates.
Not only is it desirable for a sunscreen composition to be waterproof, but such compositions should desirably also impart certain skin feel advantages. Cationic emulsions which may provide skin performance advantages have been reported in U.S. Pat. No. 4,389,418 (Burton). Therein is disclosed a water-out emulsion containing petroleum or a mineral oil to moisturize the skin, a quaternary ammonium emulsifier, a fatty alcohol and a fatty ester emollient. Greaseless skin conditioning compositions based upon cationic polymers have also been reported in U.S. Pat. No. 4,438,095 (Grollier). Among the polymers disclosed are polyamines, polyaminoamides or quaternary polyammonium compounds. Emulsions are formed wherein the aqueous phase contains the cationic polymer and there are no detergent or foaming agents present.
Diquaternary nitrogen compounds have been reported in U.S. Pat. No. 4,886,890 (Chaudhuri et al) as useful in skin lotions and shampoos. These compositions may be formulated with a variety of detergents, such as sodium laureth-4 phosphate. Personal care products incorporating cationic polysaccharides have been described in U.S. Pat. No. 4,663,159 (Brode et al). Emulsifiers in the form of phosphate quaternary compounds have been disclosed in U.S. Pat. No. 4,209,449 and U.S. Pat. No. 4,503,002, each to Mayhew et al. These emulsifiers were said to be well tolerated by human tissue, exhibiting low irritation, and were stated to be suitable for use in cosmetics.
Skin moisture retention has been significantly increased by utilizing many of the cationic compounds mentioned in the above patents. Nonetheless, there remains considerable need for improvement in moisture retention. There are also the further problems of improving mildness and of providing stability against phase separation during freeze-thaw cycles.
Although there have been significant advances in the art of waterproofing sunscreen lotions and also improving their skin moisture retention properties, there still remains considerable need for improvements. For instance, it is desirable to formulate a composition not including any hydrophobic resins. These resins leave undesirable residues upon the skin and also give rise to stability problems. Stability against phase separation during freeze-thaw cycles is an important goal for formulators. Finally, there is also the need to reduce irritancy of the sunscreen products.
Accordingly, it is an object of the present invention to provide a sunscreen composition of the waterproof variety not requiring incorporation of a hydrophobic resin.
Another object of the present invention is to provide a sunscreen composition having improved skin moisture retention.
A further object of the present invention is to provide a sunscreen composition in aqueous emulsion form whose phases resist separation even under extended freeze-thaw cycling.
A still further object of the present invention is to provide a sunscreen composition having a relatively low human irritancy.
These and other objects of the present invention will more readily become apparent from the description and examples which follow.